The present invention relates to the field of implantable hearing aid devices, and more particularly, to non-invasive positioning of implanted actuators and interconnected componentry.
Implantable hearing aid systems entail the subcutaneous positioning of various componentry on or within a patient""s skull, typically at locations proximal to the mastoid process. In semi-implantable systems, a microphone, signal processor, and transmitter may be externally located to receive, process and inductively transmit a processed audio signal to an implanted receiver. Fully-implantable systems locate a microphone and signal processor subcutaneously. In either arrangement, a processed audio drive signal is provided to some form of actuator to stimulate the ossicular chain and/or tympanic membrane within the middle ear of a patient. In turn, the cochlea is stimulated to effect the sensation of sound.
By way of example, one type of implantable actuator comprises an electromechanical transducer having a magnetic coil that drives a vibratory member positioned to mechanically stimulate the ossicular chain via physical engagement. (See e.g. U.S. Pat. No. 5,702,342). In another approach, implanted excitation coils may be employed to electromagnetically stimulate magnets affixed within the middle ear. In each of these approaches, a changing magnetic field is employed to induce vibration. For purposes hereof, the term xe2x80x9celectromechanical transducerxe2x80x9d is used to refer to any type of implanted hearing aid actuator device that utilizes a changing magnetic field to induce a vibratory response.
In the case of actuators utilizing vibratory members, precise control of the engagement between the vibratory member and the ossicular chain is of critical importance. As will also be appreciated, the axial vibrations can only be effectively communicated to the ossicular chain when an appropriate interface exists (preferably a low mechanical bias or xe2x80x9cno-load interfacexe2x80x9d) between the vibratory member and the ossicular chain. Overloading or biasing of the attachment can result in damage or degraded performance of the biological aspect (movement of the ossicular chain) as well as degraded performance of the mechanical aspect (movement of the vibratory member).
A number of arrangements have been proposed to precisely position actuators. These arrangements typically include among other things, a mechanical screw jack that controls the longitudinal movement of the actuator relative to the attachment interface. These screw jacks include a finely threaded screw that is manually adjusted, using a small tool, in or out to effect movement of a telescoping member that longitudinally positions the actuator relative to the attachment point.
Unfortunately, however, these devices suffer from several drawbacks. One drawback is that finite movements of the actuator are limited by the thread size of the screw. While it is often desirable to achieve a more finite adjustment of the actuator position, it is often not possible because of limitations in the available thread sizes. Another drawback is that regardless of tolerances in the system and screw design, a certain amount of xe2x80x9cbacklashxe2x80x9d (movement of the screw in the reverse direction when forward pressure from the adjustment tool is released) exists in the system. To compensate for xe2x80x9cbacklash,xe2x80x9d the screw is often adjusted slightly beyond the point where a desired position is reached. In some cases, several attempts at achieving the interface position must be made because of the unpredictability of the xe2x80x9cbacklashxe2x80x9d in the system.
Also unfortunately, patients may experience a xe2x80x9cdrop-offxe2x80x9d in hearing function after implantation due to changes in the physical engagement of the actuator caused by tissue growth. After implantation, however, it is difficult to readily assess the performance and adjust an implanted hearing aid actuator and interconnected componentry. For example, it is difficult to assess whether the vibratory member is in the desired physical engagement with the ossicular chain. Further, in the event of a xe2x80x9cdrop-offxe2x80x9d in hearing after implantation, it is difficult to determine the cause, e.g. over/under loading of the interface or some other problem with the hearing aid, without invasive and potentially unnecessary surgery.
In view of the foregoing, a broad objective of the present invention is to provide a method and system that provides for non-invasive assessment of the performance of implanted hearing aid actuators and interconnected componentry. A related objective of the present invention is to provide a method and system for assessing the physical interface between a vibratory member of an implantable electromechanical transducer and the ossicular chain of a patient. Yet, another objective of the present invention is to provide for implantable hearing aid actuator performance assessment in a relatively simple and straightforward manner, thereby accommodating a simple office visit evaluation.
Another broad objective of the present invention is to provide a method and system for non or minimally-invasive adjustment of implanted actuators. A related objective is to provide a method and system for repositioning an electromechanical transducer to adjust the physical interface between the vibratory member and the ossicular chain of a patient. Yet, another object of the present invention is to provide a method and system for assessing the interface between an actuator and the ossicular chain of a patient and using the assessment to non-invasively reposition the electromechanical transducer to achieve a desirable interface between the transducer and the ossicular chain of the patient.
In carrying out the above objectives, and other objectives, features, and advantages of the present invention, a first aspect is provided, which includes a method and related system for externally assessing the performance of hearing aids that include implanted actuators. The method entails the positioning of a test device external to a patient having an implanted hearing aid actuator, and the use of the test device to obtain at least one test measure indicative of an electrical signal passing through the implanted actuator. In turn, the test measure(s) is employed to assess the performance of the implanted actuator.
In this regard, the present inventors have recognized that the electrical impedance of an implanted actuator (e.g. an electromechanical transducer) is indicative of the mechanical impedance present at the interface between the actuator and the middle ear of a patient (e.g. the ossicular chain). As such, the electrical impedance of an implanted actuator may be assessed to determine whether the desired actuator/middle ear interface is present.
The present inventors have also recognized that for a given implanted actuator driven by a predetermined test signal, the electrical impedance thereof may be determined either directly, (through a measure of the voltage and current of an electrical signal passing through the actuator in response to the test signal), or indirectly (from the magnetic field generated by the actuator in response to an electrical signal passing the implanted actuator.) In the latter case, the magnetic field strength is directly related to the amount of current passing through the actuator. In turn, all other things being equal, such current is inversely related to the electrical impedance present at the implanted actuator. That is, the smaller the electrical current passing through the actuator, the larger the electrical impedance thereof. Conversely, the larger the electrical current passing through the actuator, the smaller the electrical impedance. Such electrical impedance is directly related to the mechanical impedance present at the interface between the implanted actuator and middle ear of a patient. As such, by driving an implanted actuator at one or more predetermined frequencies, the resultant magnetic field measures or voltage and current-measures may be utilized to assess whether the implanted actuator is operative and whether a desired interface between the actuator and the middle ear of patient (e.g. the ossicular chain) is present.
As may be appreciated, for a given implanted actuator driven by a predetermined test signal, the electrical impedance thereof should be within a predeterminable range when the desired actuator/middle ear interface is present. By way of a particular example, when driven at or within a predetermined range of its resonant frequency, the electrical impedance of an implanted actuator will be greater when the actuator is not operatively interfaced with the middle ear of a patient than when a desired interface is present. Stated differently, the actuator will draw more current when the desired actuator/middle ear interface is present than when no operative interface is present.
In view of the foregoing, the method and system may further provide for the comparison of the test measure(s) obtained by the test device (the test measure being indicative of the impedance of an implanted electromechanical transducer) to one or more predetermined values or ranges to assess one or more performance parameters. For example, a single test measure may be first compared to a predeterminable threshold value that confirms a first performance parameter (e.g. that the implanted hearing aid actuator and interconnected componentry are operatively functional.) In that regard, the predetermined threshold value may correspond with a minimum electrical impedance that should be present at the implanted actuator when it receives the predetermined drive signal.
Additionally, or alternatively, when a test signal is provided at or within a predetermined range of the resonant frequency of an implanted actuator, the resultant test measure(s) may be compared to a predetermined range to assess a second performance parameter. For example, the test measure(s) may be compared to a predetermined range that indicates the presence of a desirable interface between an electromechanical transducer and middle ear of a patient. In this regard, and as noted above, the predetermined range may be selected to correspond with the increased current flow through an actuator that should occur when a desired middle ear interface is present.
The inventive method and system may alternatively or also entail the provision of predetermined test signals to an implanted actuator at a plurality of different frequencies distributed across a predetermined range. In turn, by sweeping the frequency of the test signal, the corresponding test-measures that are obtained by the measurement device may be employed for performance assessment. For example, a resonant frequency may be identified and the corresponding test measure(s) utilized to determine whether the hearing aid is operational and the desired actuator/middle interface is present.
In one approach, the test device may be a measurement device non-invasively employed to measure the magnetic field generated by an implanted electromechanical transducer. As noted above, the magnetic field is directly related to the electrical current passing through the transducer and inversely related to the electrical impedance of the implanted transducer. In conjunction with this approach, a predetermined test signal may be provided to the implanted electromechanical transducer and the magnetic field measured and compared to a first threshold value to determine if the transducer is operative (e.g. to confirm that implanted componentry and interconnections therebetween are not faulty). Further, when the predetermined test signal is provided at or within a predetermined range of the resonant frequency of an implanted transducer, the resultant magnetic field test measure(s) may be compared to a predeterminable range to assess whether a desirable transducer/ossicular chain interface is present.
In one embodiment, the measurement device may comprise at least one and preferably a pair of coils for measuring the magnetic field flux passing therethrough. The magnetic field flux measurements may be provided to a test measurement device that uses the predeterminable thresholds and ranges for test measure comparisons and generation of data indicative of the test results for an audiologist or other user. The utilization of dual coils effectively provides for the cancellation of ambient electromagnetic interference that may otherwise compromise the transducer magnetic field measurements. In this regard, when dual coils are utilized, the coils should preferably be of common size and configuration, should be co-axially aligned in relation to the implanted transducer, and be configured in opposing polarity. Further, by positioning the coil(s) within a predetermined orientation range relative to an implanted transducer, the use of predeterminable thresholds and ranges for test measure comparisons is facilitated.
In another approach, voltage and current measuring circuitry may be included in the hearing aid, such as in the implanted speech processing or signal processing logic. In this case, a transmitter may also be included in the hearing aid to transmit the voltage and current measurements to the test device. The test device may use the predeterminable thresholds and ranges for test measure comparisons and generation of data indicative of the test results for an audiologist or other user.
In either of the above approaches, the test device may be employed to provide the test signal transcutaneously from an external transmitter to an implanted receiver via inductive coupling. In turn, the implanted receiver is electrically interconnected with the implanted actuator so that impedance of the actuator may be determined through the measurement of the magnetic field flux or the measurement of the voltage and current passing through the actuator.
In carrying out the above objectives, and other objectives, features, and advantages of the present invention, a second aspect is provided, which includes a method and related system for externally positioning an actuator relative to a component of the auditory system. The method entails providing electrical inputs transcutaneously via a wireless signal or inductive coupling to an implanted actuator positioning system to selectively position the actuator relative to a component of the auditory system. The electrical inputs are provided to the implanted positioning system using an external user device. In this regard, the present method and system may be utilized at the time of the initial implant of an implantable actuator to achieve a desired interface between the actuator and a component of the auditory system (e.g. the ossicular chain.) The present method and system may thereafter be utilized to non-invasively (without surgery or other similar procedure) reposition the actuator relative to the ossicular chain. The positioning system provides significant advantage when utilized with the above described assessment system in that it permits non-invasive repositioning of an actuator to achieve a desired interface in response to an assessment that the interface between the actuator and the ossicular chain has become undesirable.
In one approach, the positioning system includes a fixed member, a telescoping member and a driver. The fixed member is connected to a mounting device for mounting the positioning system to a patient""s skull. The telescoping member is connected to the fixed member and includes an actuator (electromechanical transducer) disposed on a distal end thereof. The telescoping member is movable relative to the fixed member to selectively position the actuator relative to the ossicular chain. The driver controls the selectively positioning of the telescoping member relative to the fixed member in response to electrical inputs. An externally located user device transcutaneously provides the electrical inputs to the driver. The user device may provide the electrical inputs via a wireless signal to the driver or may inductively couple the electrical inputs to the driver.
In one embodiment of the positioning system, the driver is a piezoelectric driver that includes first, second, and third piezoelectric elements. The first element cooperates with the second and third elements, which selectively clamp and unclamp the fixed and telescoping members, to selectively position the telescoping member relative to the fixed member.
As will be further described below, the present invention may be utilized in conjunction with either fully or semi-implantable hearing aid systems. In semi-implantable hearing aid applications, the predetermined test signal(s) may be provided via inductive coupling of an external transmitter and implanted receiver as noted above. The receiver output signal is then utilized to drive the implanted actuator. In fully-implantable applications, the predetermined test signal(s) may be provided via an externally located loudspeaker in the form of an audio signal that is received by an implanted microphone. The implanted microphone output signal is then utilized in driving the implanted actuator. Additional aspects, advantages and applications of the present invention will be apparent to those skilled in the art upon consideration of the following.